1. Technical Field
The present invention relates to a solid-state imaging device such as a CMOS image sensor or a CCD image sensor, its manufacturing method, and an imaging apparatus incorporating such a solid-state imaging device.
2. Related Art
In solid-state imaging devices such as CMOS image sensors and CCD image sensors, plural pixels are arranged in a semiconductor substrate in the form of a two-dimensional array and signals that are accumulated in photoelectric conversion regions of the pixels according to reception light quantities, respectively, are read out to the outside via MOS transistors (CMOS type) or charge transfer channels (CCD type).
To take a color image of three colors (R (red), G (green), and B (blue)) without using color filters, the solid-state imaging device disclosed in JP-A-2006-135252 is configured so that each pixel can detect a color image signal of one of R, G, and B. More specifically, utilizing the fact that the distance light travels in a semiconductor substrate from its surface depends on the wavelength, photoelectric conversion regions for B light detection are formed at a shallow position, photoelectric conversion regions for R light detection are formed at a deep position, and photoelectric conversion regions for G light detection are formed at a medium position.
However, the above solid-state imaging device has a problem that since the set of photoelectric conversion regions for R light detection, the set of photoelectric conversion regions for G light detection, and the set of photoelectric conversion regions for B light detection are different from each other in depth, the characteristic of the operation of drawing unnecessary charge out of each photoelectric conversion region (vacating each photoelectric conversion region) and discarding the drawn-out charge varies between these three sets of photoelectric conversion regions.
In the solid-state imaging device disclosed in JP-A-2006-310343, although color filters are used, photoelectric conversion regions for R light detection, photoelectric conversion regions for G light detection, and photoelectric conversion regions for B light detection are still formed at different positions in the depth direction in a semiconductor substrate. Therefore, this solid-state imaging device also has the problem that the charge drawing-out characteristic varies between the three sets of photoelectric conversion regions.
In the solid-state imaging device disclosed in JP-A-2007-81015, the three sets of photoelectric conversion regions have the same depth. However, each photoelectric conversion region does not extend right vertically from the surface. Instead, a deep portion is deviated from a shallow portion to one side in the horizontal direction.
This structure weakens the incident angle dependence of the range of absorption of slant incident light. Furthermore, a uniform charge drawing-out characteristic can be obtained by virtue of the constant depth. However, the deviation direction of the deep portion of the photoelectric conversion region is not adjusted according to the color, a failure may occur in color separation to cause color contamination depending on the color filter arrangement.
Recent solid-state imaging devices have more than 10 million pixels and each pixel is miniaturized nearly to the manufacturing limit. It is therefore necessary to, for example, improve the characteristic of the operation of drawing unnecessary charge from each photoelectric conversion region and suppress color contamination.